A good description contains most, if not all, the information required for a genealogical source citation and provides the information needed to properly assess the source using the Genealogical Proof Standard. In creating a source citation, genealogists are doing something closely related to an item level description, but also incorporate information from higher levels in the catalogue. A citation for the marriage certificate might be:

Church of England, St Saviour’s church, Saltley parish, County of Warwick. Original certified copy of the Marriage Register, page 109, no 217, for Joshua Arthur Smith & Beatrice Elizabeth Davis, married 23 May 1904, issued 23 May 1904. Personal archive of Sue Adams [private address on request], RWC/1/4/4. Raymond Walter Coulson (1922-1997) collection, Probate file, Winifred Clarke late Coulson, nee Smith (1906-1996) collection.

Depending on the context in which I used this certificate as evidence, I might expand the provenance information or cut it out.

Archival data standards are way ahead of genealogical data standards. Thank you for the DACS update, which I did not know about. Notable is the way this and other archival standards are working towards compatibility. Which DACS elements would you use for my marriage certificate example? I notice that you commented on my post to the Evidentia Google+ Community. Evidentia is software in development towards a source based approach to genealogical research. How do the source citation templates compare to the DACS elements for this record? Are they compatible?

There has been a good deal of discussion on genealogical data standards in the last couple of years, culminating in the formation of Family History Information Standards Organisation (FHISO). In order to make use of data in archival databases for genealogical purposes, genealogical data standards need to be compatible with archival standards. So, input from archivists is essential.

My only ‘hmmm’ comment would be that I can’t think of a repository that has materials cataloged down to the item level. It’s a highly labor intensive prospect. I can see how it works for your personal collection, but might be too much or seem daunting to someone just trying to get their collection together. Having said that, cheers to you for creating an incredible personal collection!!